The Pima Indians have a high prevalence of obesity with more than 70% of the adult population having a body mass index 27 kg/m2. Alteration in autonomic nervous system activity may contribute to the pathogenesis of obesity in this population. Studies in animal models of spontaneous obesity demonstrated decreased sympathetic nervous system activity. A recent study in obese humans showed decreased sympathetic and parasympathetic activity. The authors postulated that a disordered homeostatic mechanism promotes an excessive storage of energy by decreasing sympathetic activity. The relationship between obesity and autonomic nervous system activity will be studied in 50 Pima Indians aged 20-40 years. Fifty Caucasians of comparable age and weight will be included for comparison.